Method of producing a blended jet fuel



July 28, 1970 H. R. IRELAND METHOD OF PRODUCING A BLENDED JET FUEL FiledJune 14, 1968 2 Sheets-Sheet l A wsmohmx R M m M N e m r w N P R 6 v.6593.5 B uwmm 2 9 Et Q tm o I 6 o xm Ema 6 9:5 m: 5 6m fi cozuwm 552mm 25 m t t w 8mm 6 05 20 6 0mm B E m Age/1f July 28,1970" H. R. IRELANDMETHOD OF PRODUCING A BLENDED JET FUEL 2 Sheets-Sheet Filed June 14,1968 Gravity, AP|

United States Patent 3,522,169 METHOD OF PRODUCING A BLENDED JET FUELHenry R. Ireland, West Deptford Township, Gloucester County, N.J.,assiguor to Mobil Oil Corporation, a corporation of New York Filed June14, 1968, Ser. No. 737,146 Int. Cl. C101 1/04; C10g 39/00 U.S. Cl. 208795 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to theproduction of jet fuel. More particularly, this invention relates to theproduction of jet fuels having low freeze point and high energy contentboth on a weight basis (B.tu./lb.) and on a volume basis (B.t.u./gal).

As is well known, a jet fuel should have high temperature stability,high energy content, and good handling characteristics at both low andhigh temperatures. An acceptable jet fuel must meet rather rigidspecifications for either military or commercial use. With the passageof time, these requirements have become more demanding. For militaryuse, there is a present need for an economical jet fuel which has a highenergy content per gallon in order to increase the operating range ofthe aircraft, and a lower freeze point than exhibited by most prior artfuels in order to improve in air refueling of the aircraft. By way ofexample, a new military jet fuel specification includes the followingrequirements:

Gravity, API 44-50 Freeze point, F., max -50 Heat of combustion:

B.t.u./lb. min. 18,750 B.t.u./gal. min. 124,000 Luminometer number, min.75 Vapor pressure, p.s.i.g. and 300 F., max. 2.7 Aromatics, vol.percent, max. 5.0 Thermal stability (300/ 500/ 600 F.):

Pressure change, in Hg, max. 5 Preheater deposit code, max. 2 ThermalPrecipitation Test Pass Certain of the above specifications, forexample, the heats of combustion, and the low freeze point, as well asrestrictions upon the boiling point distribltion and vapor pressure ofthe fuel, in combination, can be satisfied only by a fuel having anarrowly defined composition. As an illustration of the interplay ofthese specifications, those skilled in the art will appreciate that aheat of combustion of 18,750 B.t.u./pound is not of itself particularlydemanding and can be met by many known jet fuel com- 3,522,169 PatentedJuly 28, 1970 positions. However, the further requirement that the fuelmust have a heat of combustion of 124,000 B.t.u./gallon eliminates manycompositions which have the required heat of combustion on a poundbasis. Fuels having a high A.P.I. gravity are characterized by lessweight per gallon, and since the heat of combustion per gallon is basedupon the weight per gallon together with the number of B.t.u. per unitweight, a low A.P.I. gravity is desirable with respect to obtaining highheat of combustion on a gallon basis. On the other hand, the heat ofcombustion per pound is ordinarily estimated as the product of theA.P.I. gravity and the aniline number (aniline-gravity product) so thata reduction in the A.P.I. gravity lowers the number of B.t.u. per pound.

It is a primary object of the present invention to provide a novel jetfuel composition which is a blend of a naphthenic jet fuel componentwith a highly paraffinic jet fuel component, with the final producthaving desirable fuel properties which are intermediate between theproperties of the two individual components. The naphthenic componenthas a low freeze point and, when employed with a relatively high freezepoint paraflinic component, is used to lower the freeze point of theblended product. The naphthenic component is also used because it has ahigh volumetric heat of combustion. However, the naphthenic fuelcomponent has a low heat of combustion on a pound basis, below thatdesired in the final product. A presently preferred paraffinic fuelcomponent has a relatively high freeze point, and is employed primarilysince it has a heat of combustion on a pound basis in excess of thatdesired in the blended product. By blending a naphthenic component and aparaflinic component. it is possible to obtain a jet fuel compositionwhich will meet standards which could not be met by either thenaphthenic component alone or the paraffinic component alone or by minormodification of either component.

The relative amounts of the two components which are blended variessomewhat depending upon the properties of each component and theproperties desired in the final product. In general, the naphtheniccomponent and the parafiinic component are present in a volume ratio ofabout 35:65 to 60:40.

It is a further object of the present invention to provide a jet fuelcomposition having a freeze point of a maximum of about -50 F., a heatof combustion of at least about 18,750 B.t.u./pound, and a heat ofcombustion of at least about 124,000 B.t.u./gallon.

In accordance with a preferred embodiment of the invention, a naphthenicjet fuel component containing about 67 to 89 vol. percent naphthenes,about 8 to 30 vol. percent paraflins, and less than about 5 vol. percentaromatics, and preferably less than about 3 vol. percent, is prepared byfractioning a highly naphthenic crude oil to obtain a kerosene fractionboiling in the range of about 380-530 F. hydrotreating the kerosenefraction in the presence of a hydrotreating catalyst to remove sulfurand nitrogen compounds to thereby improve the thermal stability of thekerosene fraction, separating the resulting normally gaseous andnormally liquid fractions, and removing at least a substantial portionof the aromatic hydrocarbons from the liquid fraction, for example, bysulfur dioxide extraction, to obtain the desired naphthenic 3 jet fuelcomponent. The naphthenic component is blended with a parafiinic jetfuel component containing about 3- 17 vol. percent naphthenes, up toabout 5 vol. percent preferably, about 2-3 vol. percent aromatics, andthe remainder being substantially paraflins. The paraffiniccomponent hasa heat of combustion of about 18,850-

18,960 B.t.u./pound. The paraffinic jet fuel component is prepared byrefining a kerosene fraction containing at least about 40% (vol.)paraffins at a temperature of about 790-870 F. under conditions todehydrogenate and isomerize naphthenes and to isomerize normal paraffinswhile maintaining at least 75% paraffin retention, separating thenormally gaseous and normally liquid fractions from the refiningtreatment, extracting at least a substantial portion of the aromatichydrocarbons from the liquid fraction, for example, by sulfur dioxideextraction, to obtain a raffinate comprising the paraffinic jet fuelcomponent.

The blended jet fuel composition has a heat of combustion of at leastabout 123,000 B.t.u./gallon, preferably 124,000 B.t.u./gallon and a heatof combustion on a pound basis of at least about 18,700 B.t.u./ pound,prefferably 18,750 B.t.u./ pound, and a freeze point of a maximum ofabout 50 F.

The invention will be described in further detail in connection with theaccompanying drawings in which:

FIG. 1 is a simplified flow sheet of a process for preparing a jet fuelcomposition in accordance with the invention; and

FIG. 2 is a graph illustrating the relationship between the A.P.I.gravity of the product and the heat of combustion of the product.

Referring now to the drawing, and more particularly to FIG. 1, apreferred embodiment of the invention will now be described.

PRODUCTION OF NAPHTHENIC FUEL COMPONENT Coastal A Cal. MIX

Pro erties:

Gn'avity, API.. 32.0 35. 1 Aniline Point, F- 130 130. Freeze Point, F 767b Composition:

Paraflins, vol. percent 9 1 6 Naphthenes, vol. percent. 79 (15 Aromaticsvol. percent 12 19 Distillation AsTM, F.-

IBP 399 371 417 407 443 445 90 488 496 End point 527 530 The kerosenefraction is passed from the fractionator to a multiple zone reactorwhere the kerosene fraction is hydrotreated to improve its thermalstability by hydrogenation of olefius, if present, and removal ofnitrogen and sulfur compounds and other impurities, for example, byhydrogenation of pyridine to ammonia and by hydrogenation of thiopheneto hydrogen sulfide. The hydrogenation is carried out in the presence ofa catalyst which may be a known catalyst employed for treatment ofpetroleum fractions in order to hydrogenate olefius, tohydrodesulfurize, etc. Examples of such catalysts are Group VI and GroupVIII metals, oxides and sulfides, usually supported upon an inert porouscarrier such as activated alumina. Mixtures of Groups VI and VIII metaloxides and sulfides are particularly advantageous. Exemplary catalystsinclude cobalt molybdate and nickel molybdate on alumina which are theparticularly preferred catalysts of the invention.

The hydrogenation and desulfurization treatment is carried out attemperatures between 550 and 750 F., preferably between about 580-675 F.and at a space velocity of up to 5.0, a hydrogen partial pressure ofabout 450 to 800 p.s.i.g., and a hydrogen recyycle rate of about 5003000s.c.f./bbl. Although not illustrated on the simplified flow sheet, itwill be understood that the products from the reactor are passed to aseparator from which hydrogen is recycle, preferably after removal ofhydrogen sulfide and other impurities; and after stripping off lightends the normally liquid fraction is passed to an extractor. In theextractor, the liquid fraction is contacted with a suitable solventwhich is selective for aromatic hydrocarbons, for example, sulfurdioxide, which is the preferred solvent. The conditions employed duringthe solvent extraction are substantially conventional. Thus, whenemploying liquid sulfur dioxide as the solvent, the sulfur dioxide maybe employed in a ratio of about to about 300 volume percent based on thefraction being extracted, and the temperature may be in the range ofabout 20 to 50 F.

The rafiinate from the extractor is then percolated for example throughclay, or bauxite to yield a highly naphthenic jet fuel componentcontaining about 67 to 89 vol. percent naphthenes, about 8 to 30 vol.percent parafiins, and less than about 3 percent aromatics.

The naphthenic jet fuel component has a freeze point less than that ofthe freeze point desired in the final blended product and is usually inthe range of less than 76 to 60 F., preferably below 68 F. Thenaphthenic jet fuel component has a net heat of combustion of less thanabout 18,700 B.t.u./ pound.

PRODUCTION OF PARAFFINIC FUEL COMPONENT Perhaps the principal functionsof the paraflinic jet fuel component are to elevate the heat ofcombustion in B.t.u./ lb. and luminometer number of the blended finalproduct. In accordance with the present invention, the paraffiniccomponent is prepared from selected petroleum hydrocarbon fractions ofthe kerosene type composed substantially of hydrocarbon mixtures boilingin the range from about 370 to about 550 F., preferably from about 380to about 530 F., and containing at least about 40 Weight percentparafiins. Specific embodiments of suitable feed stocks include straightrun kerosene fractions of the following compositions:

ASTM BOILING RAN GE (375500 F.)

The kerosene fractions described above are subjected to a lowtemperature mild catalytic refining treatment carried out undercorrelated reaction conditions in the presence of a dehydrogenationcatalyst such that the predominant reactions are dehydrogenation ofnaphthenes and isomerization of normal paratfins in the feed stock withat least 75% parafiins retention; that is, cracking is minimized. Theresulting liquid fraction which boils generally within the same range asthe feed is then solvent extracted to remove at least a substantialamount of the aromatics, which aromatics may be those originally presentin the feed as well as those formed during the refining treatment, toprovide a raffinate constituting the paraffinic jet fuel component.

Where necessary, the feed stocks may be treated prior to the refining toremove impurities which would contaminate the catalysts used in therefining treatment and/or which would cause corrosion problems. Thus,feed stocks containing a relatively high concentration of sulfur arepreferably pretreated to reduce the sulfur concentration to not morethan about 20 parts per million, along with substantially completeremoval, when present, of other undesirable impurities includingnitrogen, arsenic and lead. To effect this removal, the feed stock maybe subjected to hydrodesulfurization by treatment with a suitablehydrodesulfurization catalyst (e.g. cobalt molybdate on sulfurizationcatalyst.

Space velocity (LHSV) 4 Hydrogen partial pressure, p.s.i.g 450Temperature, F. 700 Hydrogen circulation rate (s.c.f./bbl.) 1000 It willbe understood that the desulfurization conditions may be varieddepending upon the particular feed stock employed, and suitable moregeneral operating conditions are indicated below.

Space velocity (LHSV) 0.5-10

Hydrogen partial pressure (p.s.i.g.) 250-800 Temperature, F. 600-800Hydrogen circulation rate (s.c.f./bbl.) 190-3000 Following thedesulfurization pretreatment, the reaction products are passed to astripper where the gaseous phase rich in hydrogen, and containingsubstantially all of the hydrogen sulfide and ammonia produced in thepretreater, is stripped from the liquid phase, for example, by employinga stream of recycle gas from the reformer. The liquid phase is thenpassed to a multistage reformer which, for the purpose of illustration,is ShOWn in FIG. 1 as having three stages.

In the reformer, the feed stock is subjected to mild catalytic treatmentunder correlated conditions to provide selective dehydrogenation of Cring naphthenes to aromatics, isomerization of alkyl C ring naphthenesto C ring naphthenes which are then aromatized, and isomerization ofnormal paraffins to isoparafiins, while minimizing cracking. Theconditions are correlated to obtain at least 75% parafiin retention, andpreferably at least about 95% paraffin retention.

The reformer treatment conditions can be varied depending upon theparticular feed stock employed, and upon the desired properties of theparaffinic fuel component to be produced, which properties arecorrelated with the properties of the particular naphthenic fuelcomponent which will be blended therewith to obtain the final blendedproduct. In general, the conditions are within the following ranges:

Space velocity (LHSV) 0.5-6 H /feed, s.c.f./bbl. 400010,000 Averagetemperature, F. 790-870 Hydrogen pressure, p.s.i 300-800 In theillustrated embodiment in which the catalytic treatment is carried outin three stages, in the first stage, the feed stock is treated underconditions to effect substantial naphthene isomerization anddehydrogenation with only a nominal amount of other reactions such ascracking or isomerization of paraifins. The temperature of the feedentering the first stage may be about 870 F. while the temperature ofthe fraction leaving the first stage is in the order of 790 F. since thedehydrogenation "reaction consumes heat. It will be understood thatreference to a three stage treatment is intended to include differentcatalytic reaction zones within a single reactor, or in separatereactors, each of which contains a catalyst (e.g. a bed of catalyst),with the reaction zones being interconnected by transfer lines for thepassage of product from one reaction zone to the other, which transferlines are equipped with heaters for heating the product from onereaction zone prior to its introduction into the succeeding reactionzone. In the second and third reaction zones, the conditions areregulated to achieve primarily isomerization of normal paraffins toisoparaffins accompanied by some further dehydrogenation of anynaphthenes which may still be present. The feed to the second reactionzone may be heated to about 830 F., and the product leaving the secondreaction zone which may be at a temperature of about 810 F. ispreferably again reheated, for example, to about 820 F. beforeintroduction into the third reaction zone. The product from the thirdreaction zone may be at a temperature of about 810 F.

It will be understood that, for any given kerosene feed stock passed tothe reformer, as the average reaction temperature employed increasesfrom the lower to the higher side of the stated temperature range, thespace velocities generally increase within the stated range. Inaddition, as the catalyst ages, the temperature is generally increasedat constant space velocity, or alternatively, the space velocity isdecreased while maintaining a substantially constant average temperaturein order to maintain a substantially constant quality of reformedproduct.

The catalyst employed in the reformer is a dehydrogenation catalysthaving selectivity for the isomerization and the dehydrogenation ofnaphthenes, and having low cracking activity.

For the catalytic treatment of the feed stocks embodied suitablecatalysts are metals of the platinum series and particularly, platinum,on carriers such asaIumina. Specific examples thereof are catalysts, oflow cracking activity, comprising from about 0.1 to about 1.0 percentplatinum on alumina (e.g. eta alumina) or on a low activitysilica-alumina base and which may contain a suitable halogen (e.g.chlorine) in an amount of up to about 1.0% and, preferably, in an amountnot greater than the platinum content, and preferably lower. Suchcatalysts that contain from about 0.3 to about 0.8% platinum areparticularly suitable. In a broader aspect, however, suitable for useherein are catalysts which, as is known to those skilled in the art,possess activity for dehydrogenating naphthenes to aromatics and are oflow cracking activity and, as further examples, such catalysts includetungsten and/ or nickel on kieselguhr, chromium oxide on alumina, andothers.

The reformate is passed to an extractor for reduction of the aromaticconcentration, for example, by extraction with liquid sulfur dioxide.The conditions employed during the solvent extraction may besubstantially the same as those employed during the corresponding stepin treating the naphthenic jet fuel component, that is, when sulfurdioxide is the solvent, the sulfur dioxide may be employed in a ratio ofabout 100 to about 300 volume percent, based on the fraction beingextracted, at a temperature in the range of about 20 to 50 F.

The raflinate from the extractor is then percolated through bauxite toimprove its thermal stability and to yield the desired paraffinic jetfuel component which, in its own right, has found use as a jet fuelmeeting different specifications than those which are met by the blendedproduct of the present application. The parafiinic jet fuel component ofthe invention contains about 317 vol. percent naphthenes, a maximum ofabout 5 vol. percent, preferably about 2-3 vol. percent aromatics, andhas a freeze point in the order of about 40 to 45 F. and a heat ofcombustion of about 18,85018,960 B.t.u./ pound.

Other suitable paraflinic blending components include a hydrogenatedheavy alkylate, and a paraffinic hydroisomerized product such ashydroisomerized wax or paraffinic hydrocrackate. The heavy alkylateblend stock is prepared by hydrogenating olefins in a heavy alkylatefraction boiling in the range of about 380550 F. employing processingconditions substantially the same as those described above for thehydrogenation and desulfurization of the naphthenic stock. Theparafiinic hydroisomerized product may be employed as is. These blendstocks have the advantage of having low freeze points. The properties ofthese blend stocks, and suitable hydrogenation conditions for thealkylate are set forth in the following table.

PROPERTIES OF PARAFFINIC BLEND STOCKS Heavy Hydro- Alkylate crackateProcessing Conditions Hydrogenation of olefins:

H2 Recycle, s.c.fJb LHSV, v./hr./v Temperature, F-

BLENDING OF NAPHTHENIC AND PARAFFINIC COMPONENTS In order to achieve ablended jet fuel composition having the desired properties, thenaphthenic jet fuel component and the paraflinic jet fuel component areblended in a volume ratio of between about 35:65 to 60:40, and where itis intended to meet the aforementioned military specifications includingthe heat of combustion of about 124,000 B.t.u./ gallon, these componentsare blended within the aforementioned ranges to give a product having agravity of about 46.0 to 47.0 API.

In order to make the specification of 18,750 B.t.u./ pound, the blendedjet fuel should have a paraffin content between 50-62 vol. percent.About 50 vol. percent paraffins will make the specification when theamount of aromatics is about 2 vol. percent, this being a typicalminimum aromatic content following sulfur dioxide extraction. A parafiincontent of about 62 vol. percent will make the specification when thearomatics content is at its maximum permissible value of 5 vol. percent.In addition, at least about 50 vol. percent paraifins is required in theblended jet fuel in order to give a luminometer number of 75 or betteras required by the specifications.

Referring to FIG. 2, in order to make the two heat of combustionspecifications, it is necessary to operate above the 18,750 B.t.u./pound line and to the left of the 124,000 B.t.u./ gal. line. In orderfor the blended product to have the necessary composition, the gravitymust be maintained between 46.0 to 47.0 API. To meet these restrictionsit is necessary to operate within the shaded area shown on FIG. 2.

In order to have a freeze point of 50 F. or less, the components shouldbe blended to provide a product having a maximum of about 16.5% normalparaifins. It will be appreciated that, in addition to adjusting therelative amounts of the two components, the normal parafiin content maybe varied by way of the treatment of the paraffinic component in thereformer to isomerize normal paraffins.

It will also be appreciated that, if specifications permit, conventionaljet fuel additives may be added to the blended product. Suchconventional additives include oxidation inhibitors and metaldeactivators.

The invention will further be described with reference to the followingexample.

EXAMPLE A naphthenic fuel component is prepared by introducing Cal. mix,the mixture of three California crudes as described previously, into afractionator and recovering a kerosene fraction boiling within the rangeof 380530 F. The kerosene fraction is passed to a reactor where it ishydrotreated at a hydrogen pressure of 650 p.s.i.a., a LHSV of 1.9v./hr./v., a hydrogen circulation rate of 2000 s.c.f./bbl., atemperature of 626 F., and in the presence of a cobalt molybdatecatalyst. The normally liquid fraction is recovered and passed to anextractor where aromatics are removed by sulfur dioxide extractionemploying a ratio of sulfur dioxide of 250 vol. percent based on thefraction being extracted and a temperature of 4 F. The rafiinate fromthe extractor is then percolated through clay to improve its thermalstability and to obtain the desired naphthenic jet fuel component.

A paraflinic fuel component is prepared from a straight run kerosenefraction which is pretreated to remove impurities in a pretreater at ahydrogen pressure of 700 p.s.i.a., a LHSV of 2.0, a hydrogen circulationrate of 2000 s.c.f./bbl., a temperature of 700 F., and in the presenceof a cobalt molybdate hydrodesulfurization catalyst. After removal ofthe gaseous phase in a stripper, the normally liquid fraction is passedto a three stage reformer where isomerization and dehydrogenation ofnaphthenes and isomerization of paraffins is carried out with onlynominal amounts of other reactions such as cracking. The feed enters thefirst stage of the multi stage reformer at a temperature of 870 F. andleaves at 790 F. After reheating to 830 F., the feed passes to thesecond zone from which it exits at 810 F., and is reheated to 820 F.,for introduction into the third and last zone from which the productleaves at 810 F. The normally liquid product from the reformer is passedto an extractor where aromatics are removed by sulfur di oxideextraction employing sulfur dioxide in a ratio of 250 vol. percent basedon the fraction being extracted, at a temperature of 4 F. The rafiinateis then percolated through bauxite to improve its thermal stability andthe desired paraffinic jet fuel component is thus obtained.

The naphthenic and paraffinic components are then blended to produce ablended jet fuel composition.

The properties of three blended jet fuel compositions prepared byblending naphthenic and paraffinic components as described above are setforth in the following table.

BLENDED .TET FUEL COMPOSITIONS Blend 1 Blend 2 Blend 3 Components:

Paratfinie Component, vol. percent 56. 58. 5 62 Naphthenic Component,vol. percent 43. 5 41. 5 Topped Naphthenic Component, 1 vol. percent 38Properties:

Gravity, API 46. 6 46. 6 4G. 6 Aniline Point, F- 170.0 170. 5 172. 3Total Absorption, v 2. 6 3. 3 3. 0 Heating Value:

B.t.u./lb. (AX G) 18, 753 18, 755 765 B.t.u./lb. (Calorimeter) 18. 77018,760 18, 780 Btu/gal 124, 050 124, 060 124, 130 Freeze Point, F 51 5150 Freeze Point of Paralfinic Component, F -41 45 Freeze Point of Naphthenic Component, F- ---70 68 Distillation, ASIM, F.:

IBP 370 377 411 10 409 405 421 20... 418 411 424 50-.- 433 426 437 70447 441 449 90 476 470 476 EP 514 502 515 1 Before blending, thenaphthenic component was topped.

What is claimed is:

1. A process for preparing a jet fuel having a freeze point below about40 F. and a heat of combustion on a weight basis of at least 18,700Btu/pound which comprises:

(a) hydrotreating a naphthenic kerosine fraction containing less thanabout 30 vol. percent paraffins and boiling in the range of from about380 F. to about 530 F. under conditions to provide a naphthenic jet fuelcomponent of improved thermal stability.

(b) reforming a kerosine fraction containing at least about 40 vol.percent paraffins in the presence of a catalyst and operating conditionseffective to dehydrogenate and isomerize naphthenes, isomerize parafiinsand retain at least vol. percent of the parafiins in the feed duringisomerization thereof to produce a paraflinic product component, and

(c) blending said naphthenic jet fuel component with said paraffinproduct component after reduction in aromatic content in a volume ratiobetween about 35:65 to 60:40 to produce jet fuel having a heat ofcombustion of 124,000 B.t.u./gal., an aromatic content less than 5 vol.percent and a freeze point of at least 40 F.

2. A process according to claim 1, wherein said naphthenic jet fuelcomponent contains about 67 to 89 vol. percent naphthenes, about 8 to 30vol. percent parafiins, and less than about 5 vol. percent aromatics.

3. A process according to claim 1, wherein said paraifinic jet fuelcomponent has a freeze point of about -40 to 45 F.

4. A process according to claim 1, wherein said naphthenic kerosinefraction is hydrotreated to improve its thermal stability at about 5 to675 F at a hydrogen pressure of about 450 to 800 p.s.i.a., and a liquidhourly space velocity of up to about 5.0.

5. The process of claim 1 wherein the preparation of product componentaccording to (a) and (b) includes the step of extracting aromatics fromthe kerosine fuel with sulfur dioxide.

References Cited UNITED STATES PATENTS 2,910,426 10/1959 Gluesenkamp etal. 208-143 3,231,628 1/1966 Bloch 20815 3,367,860 2/1968 Barnes et al.208-15 3,384,574 5/1968 Halik et al. 208-15 HERBERT LEVINE, PrimaryExaminer U.S. Cl. X.R.

